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Johnson 40 HP starts and idles...but no power under load

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  • 1 Post By kitebuz

Johnson 40 HP starts and idles...but no power under load

Old 07-07-2019, 07:55 AM
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Default Johnson 40 HP starts and idles...but no power under load

Greetings,
I am still working on what has turned into a project boat...a Princecraft Holiday DLX with a 2000 Johnson 40 HP outboard.
Took awhile but finally got to test it on the river today, the motor starts (a little tough, but I'll get better at it) and idles fine.
After warming up, it came up on plane and took off no problem......but I came around a bend and a pontoon was close by so I quickly slowed down.
After that it would not come back up on plane, full throttle didn't really do anything. Adjusted tilt and trim, no help.
New plugs, fresh gas, twin carbs have been adjusted......going out to pull the gas filter now, any other suggestions / help?
Thanks,
Jim
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Old 07-07-2019, 09:53 AM
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Is the timing arm advancing ? Move the throttle and observe it's movement.
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Old 07-07-2019, 12:13 PM
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Is there a way to hook up to a remote tank. Even if you put fresh gas in, what was in the tank before?
Also being a project boat I bet it has sat with older fuel lines and bulb. Buy new ones. Checking filter is a good start as you mentioned.

Jets in carbs of small 2 stroke outboards are tiny, it does not take much to clog.
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Old 07-07-2019, 07:06 PM
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Thank you for the replies gentlemen.
Is the timing arm advancing ? Move the throttle and observe it's movement.
I watched the full movement from slow to WOT, Everything is moving smoothly, including under the flywheel. There appears to be more room for travel in the fast direction.
The boat did come up on plane and ran fast, briefly, then I had to cut back and could not return to that state. Engine ran the whole time, whether in forward, neutral or reverse.

Is there a way to hook up to a remote tank.
Yes, already there checked the fuel lines: good. Compression test and cleaning the carbs are next.
The engine will sit and idle until I turn off the key. Kill switch is inoperable......it's on the list.
Thanks,
Jim
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Old 07-08-2019, 08:11 AM
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When you advance throttle, the rpms do not increase?

Do the throttle plate(s) open when you advance the throttle?
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Old 07-10-2019, 05:40 AM
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Both plates open fully. Initially the RPM's increased and the boat took off. Then, not so much.....I purchased carburetor rebuild kits and am doing them today, right after a compression check.

In the meantime , what's the round thing between my squeeze bulb and my tank? Never had one on a tank before.... just another question mark to me. Can I discard to eliminate it as a problem. ?
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Old 07-10-2019, 05:50 AM
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Originally Posted by Happy Fisherman View Post
Both plates open fully. Initially the RPM's increased and the boat took off. Then, not so much.....I purchased carburetor rebuild kits and am doing them today, right after a compression check.

In the meantime , what's the round thing between my squeeze bulb and my tank? Never had one on a tank before.... just another question mark to me. Can I discard to eliminate it as a problem. ?
That round thing looks like it might be a fuel filter. There appears to be a transparent filter element bowl beneath the grey cover. If that's what it is, it's unnecesary and I would remove it.

The clamp on the "filter" outlet appears to be loose. An air leak at a fuel line fitting could be the cause of your problems. The line might not leak under pressure, but leak when the outboard pulls a vacuum on the fuel line- I've seen that before.
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Old 07-10-2019, 01:33 PM
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That's a EPA abomination.Does the fuel tank have a vent ?
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Old 07-10-2019, 02:53 PM
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Removed both carbs, they looked pretty good, but since they were out and I had the kits we cleaned and rebuilt them.
The compression came back almost exactly 150psi on both cylinders (some good news)...lake test.....still no power in gear.
The RPM's are not increasing when opening the throttle in gear. We adjusted the idle mix ...but there is no throttle mix.

That's a EPA abomination.Does the fuel tank have a vent ?
LOL...hard to believe I can laugh at this point but that elicited a chuckle.......No vent, I have been loosening the cap to make sure its breathing....already moved on to another tank.

The clamp on the "filter" outlet appears to be loose. An air leak at a fuel line fitting could be the cause of your problems. The line might not leak under pressure, but leak when the outboard pulls a vacuum on the fuel line- I've seen that before.
I'm already onto another tank with a normal gas line & (more) fresh gas.....also changing the lower unit oil.

Thanks for the replies, I'm leaving for vacation with the grandsons on Saturday, so my window is fast closing......
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Old 07-10-2019, 03:47 PM
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Do you have a timing light? If so, launch the boat with engine cover removed and timing light connected to cylinder #1. Check the timing at idle, then advance the throttle and watch for the timing to advance. If the timing does not advance, you are on the track of the problem. If the timing does advance, we still have a mystery, but determine the timing at WOT. In a typical outboard, the amount of advance at WOT should be ~30 degrees compared to timing at idle.
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Old 07-11-2019, 10:49 AM
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had similar problems once before and it was a crankcase leak. It was a POS boat and just trashed it, not sure how to advise checking that other than a leakdown test.
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Old 07-11-2019, 11:14 AM
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If you have a timing light, check both cylinders for spark at idle, then as you advance the throttle. A failing coil can work fine at low RPMs, but fail as they increase.

With no timing light, pull a plug wire off, it will normally still run on one cylinder. Throttle it up, If it runs on one and not the other, then you at least know where to start looking.

Also, you can put your hand over each carb intake, just slightly block the flow, if it runs better you have a fuel restriction someplace.
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Old 07-11-2019, 11:30 AM
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Did you clean the jets in the carb w/ a wire strand? I would. Seems like I go thru this at the start of each season w/ my 25hp. I pull a single strand of wire from a piece of 14 awg marine wire, and run it thru every passage I can after removing the hi & low idle screws. I also spray with carb cleaner, then have at it with compressed air. Had this same issue a month ago, did the clean, and it runs like a top.
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Old 07-11-2019, 03:54 PM
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Originally Posted by kitebuz View Post
Did you clean the jets in the carb w/ a wire strand? I would. Seems like I go thru this at the start of each season w/ my 25hp. I pull a single strand of wire from a piece of 14 awg marine wire, and run it thru every passage I can after removing the hi & low idle screws. I also spray with carb cleaner, then have at it with compressed air. Had this same issue a month ago, did the clean, and it runs like a top.
I use the garden hose with a spray nozzle until i physically see every little opening in the carb bore mist.It also doesn't burn your skin or eyes.
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Old 07-12-2019, 09:13 PM
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Red face May have found the issue....

Hello,
Sorry for the delay in replying, family health issues...life has a funny way of reminding me what is really important.
But vacation is still on so all's well that ends well.
Thanks so much for the tips and suggestions, really appreciate the responses. We used wires wires and high pressure air when we rebuilt the carbs.

(Aside- when we were trying to fix this issue my son-in law and I were (obviously) scouring the internet to see who else was getting their arse kicked. We did find one
common theme : Although there were plenty with almost the same problem....the actual fixes were never posted.)
Now I know why......it's so embarrassing.
When I bought the new fuel filter , the lady says don't forget about the arrow.....(a thin white arrow on a white body, honestly never saw it, although, yes of course there is a direction of flow)
My friend ends up putting it on exactly as the old one is on......backwards! OMG!
I found it/remembered to look the next day while replacing the gas lines and bulb ( fyi, the round thing on the old fuel line is an anti return or backflow valve).
So , although I have not had the opportunity to test it under load, I'm hoping this is the fix....since everything else we checked seems right...never did get to the timing light.
So the boat is coming on vacation and my grandson will be so happy to go fishing on our boat. Here is a pic, not a finished product, but it's getting there.
Thanks for all the help......


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